The aim of the proposed research is to investigate emotional influences on the perception of spatial layout, and more specifically, how fear influences the perception of heights. In a representative study, participants would stand on a high balcony and would provide indices of the apparent distance to the ground. This research is based on recent work, which showed that the perception of spatial layout was influenced by the physiological state of the observer (Proffitt, Bhalla, Gossweiler, &Midgett, 1995;Bhalla &Proffitt, 1999;Proffitt, Stefanucci, Banton, &Epstein, 2003). For instance, observers who wore a heavy backpack saw slants as steeper and distances as farther than those who did not wear a backpack. Recent work has shown that fear also influences the perception of relevant spatial layout. Steep hills, which would be impossible to descend on foot, appear steeper when viewed from the top than from the bottom. Steep hills also appear steeper when viewed from the top while standing on a skateboard as opposed to standing on a box of equivalent height. Establishing a relationship between emotion and perception would not only extend our understanding of perception, but would also provide insights into the nature and treatment of fears and phobias. Traditionally, the focus has been on relatively higher-level cognitive processing, such as biases in attention and memory. In a sense, we seek to show that fearful individuals literally see the world through a "distorted lens." To test this hypothesis, we will conduct three sets of studies. First, we will determine the parameters for normative height perception. We will employ various methodologies to obtain assessments of perceived height in both the real world and virtual reality. Assessments of fear and postural sway will also be collected and correlated with the apparent height measures. The norms and measures established will be used in the subsequent studies. Next, we will conduct a series of studies to determine if increases and reductions in state-level fear produce differences in height estimation. We will also test alternative hypotheses by introducing arousal and alternative mood manipulations. We predict that perceived height will increase when participants are frightened, but not when they are aroused for different reasons or in different moods. These experiments will allow us to better understand the underlying mechanisms by which fear affects perception of height. Finally, we will assess whether phobias influence estimates of height. Specifically, we will investigate whether individuals with a specific phobia toward heights (termed acrophobia) show larger changes in height estimation relative to other-fear and control groups. We will also test whether fear reduction (after habituation of fear through exposures) attenuates the overestimation of heights expected in persons with acrophobia.